The present invention relates to engine control systems, and more particularly to engine control systems for internal combustion engines with a catalytic converter.
In order to reduce emissions, modern car engines carefully control the amount of fuel that is burned. The engines control the air-fuel mixture to achieve an optimum stoichiometric ratio. At the optimum stoichiometric ratio, all of the fuel is burned using all of the oxygen in the air. For internal combustion engines, the stoichiometric ratio is about 14.7:1. In other words, for each pound of gasoline, 14.7 pounds of air is burned. The air-fuel mixture varies from the optimum stoichiometric ratio during driving. Sometimes the air-fuel mixture is lean (an air-to-fuel mixture higher than 14.7), and other times the air-fuel mixture is rich (an air-to-fuel mixture lower than 14.7).
The primary emissions of a car engine are nitrogen, carbon dioxide and water vapor. Air is approximately 78 percent nitrogen (N2) gas. Most of the nitrogen passes through the car engine. Carbon dioxide (CO2) is produced when carbon in the fuel bonds with the oxygen in the air. Water vapor (H2O) is produced when hydrogen in the fuel bonds with the oxygen in the air.
Because the combustion process is never perfect, some additional harmful emissions are also produced by car engines. Carbon monoxide (CO), a poisonous gas that is colorless and odorless, is produced. Hydrocarbons or volatile organic compounds (VOCs), resulting from unburned fuel that evaporates, are produced. Sunlight breaks these emissions down to form oxidants that react with oxides of nitrogen to cause ground level ozone (O3), a major component of smog. Oxides of nitrogen (NO and NO2, together called NOx) contribute to smog and acid rain and cause irritation to human mucus membranes. Catalytic converters are designed to reduce these three harmful emissions.
Most modern cars are equipped with three-way catalytic converters. xe2x80x9cThree-wayxe2x80x9d refers to the three harmful emissions that catalytic converters help to reducexe2x80x94carbon monoxide, VOCs and NOx. The catalytic converter uses two different types of catalysts, a reduction catalyst and an oxidization catalyst. Both types include a ceramic structure that is coated with a metal catalyst, usually platinum, rhodium and/or palladium. The catalytic converter exposes the catalyst to the exhaust stream while minimizing the amount of catalyst that is required due to the high cost of the catalyst materials.
There are two main types of structures that are used in catalytic convertersxe2x80x94honeycomb and ceramic beads. Most cars today use a honeycomb structure. The reduction catalyst is the first stage of the catalytic converter that typically uses platinum and rhodium to help reduce the NOx emissions. When the NOx molecules contact the catalyst, the catalyst separates the nitrogen from the molecule, holds on to the nitrogen and frees the oxygen in the form of O2. The nitrogen bonds with other nitrogen that are also held by the catalyst, forming N2:
2NO= greater than N2 +O2 or 2NO2= greater than N2+2O2
The oxidation catalyst is the second stage of the catalytic converter that reduces the unburned hydrocarbons and carbon monoxide by burning (oxidizing) them over a platinum and palladium catalyst. The oxidation catalyst reacts the CO and hydrocarbons with the remaining oxygen in the exhaust gas:
2CO+O2= greater than 2CO2
The third stage is a control system that monitors the exhaust stream and uses the information to control the fuel injection system. Typically, an oxygen sensor is mounted between the engine and the catalytic converter. The oxygen sensor senses oxygen in the exhaust. An engine control system increases or decreases the amount of oxygen in the exhaust by adjusting the air-fuel mixture. The engine control system operates the engine at close to the optimum stoichiometric ratio. The engine control system provides enough oxygen in the exhaust to allow the oxidization catalyst to burn the unburned hydrocarbons and CO.
While the catalytic converter reduces pollution, the catalytic converter can still be improved substantially. The catalytic converter must be heated to a fairly high temperature before operating. When a car is started, the catalytic converter does not reduce the pollution in the exhaust until the catalytic converter reaches a predetermined temperature that is also called the light-off temperature.
One conventional solution to the delay is to move the catalytic converter closer to the engine. The hot exhaust gases reach the catalytic converter more quickly and heats the catalytic converter faster. This approach tends to reduce the life of the catalytic converter by exposing the catalytic converter to extremely high temperatures. Most carmakers position the catalytic converter under the front passenger seat, far enough from the engine to keep the temperature down to levels that will not harm it.
Preheating the catalytic converter is another conventional way to reduce emissions. The easiest way to preheat the converter is to use electric resistance heaters. Unfortunately, the 12-volt electrical systems on most cars do not provide enough energy to heat the catalytic converter fast enough. Most drivers will not wait several minutes for the catalytic converter to heat up before starting their car.
A vehicle engine control system and method according to the present invention controls an engine that includes a plurality of cylinders and that generates exhaust gas. An air-assisted direct injection fuel system supplies an air/fuel mixture to the cylinders. A catalytic converter reduces harmful emissions from the exhaust gas after the catalytic converter reaches a light-off temperature. A controller communicates with the engine and the air-assisted direct injection fuel system. The controller deactivates at least one of the cylinders of the engine before the catalytic converter achieves the light-off temperature to hasten light-off of the catalytic converter.
In another feature of the invention, a vehicle engine control system and method controls an engine that includes a plurality of cylinders and that generates exhaust gas. An air-assisted direct injection fuel system supplies an air/fuel mixture to the cylinders. A catalytic converter that reduces hydrocarbon emissions from the exhaust gas after the catalytic converter reaches a light-off temperature. A controller modifies cam phasing, varies the average air/fuel mixture, and retards spark angle to hasten catalytic converter light-off.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.